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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Toxicity to algae: 70.5 hr EC50 >988 mg/l and NOELR: ≥988 mg/l (nominal) (highest concentration tested) (guideline ISO 10253 (Water quality - Marine Algal Growth Inhibition Test with Skeletonema costatum and Phaeodactylum tricornutum)).

Key value for chemical safety assessment

Additional information

A 70.5-hour EL50 of >988 mg/l and NOELR of ≥988 mg/l (nominal) (highest concentration tested) have been determined for the effects of the registration substance on growth rate of the marine algal species Skeletonema costatum. These values are above the water solubility limit of the substance (0.0073 – 0.0088 mg/l at 23°C) and indicate that toxic effects on algae are unlikely to occur at this concentration. For monoconstituent substances it would not normally be appropriate to test at concentrations above the solubility limit.

This is the only reliable study available for this substance and it has been chosen as key.

A 72-hour EC50 value of >89 mg/l (measured (TWA)) has been determined for the effects of read-across substance trimethox(vinyl)silane (CAS 2768-02-7) on growth rate of Pseudokirchneriella subcapitata. The data indicate that the vinyl side chain is unlikely to contribute significant excess ecotoxicity to the substance.

The data above are supported by read-across evidence relevant to the impurities. The registration substance has an average purity of >80% Vi4-D4, with <15% 2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane Vi5-D5 (CAS 17704-22-2; Impurity 1) and <10% 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane Vi3-D3 (CAS 3901-77-7; Impurity 2) present as impurities. After due consideration of the properties, the presence of these impurities is not expected to affect the overall hazard profile of the substance. Read-across studies are in place as supporting studies, to consider the properties of the impurities. Data for Vi5-D5 are read-across from decamethylcyclopentasiloxane D5 (CAS 541-02-6), data for Vi3-D3 are read-across from hexamethyltrisiloxane D3 (CAS 541-05-9). These siloxanes have similar properties with regard to aquatic ecotoxicity.  Further information is given in a supporting report (PFA, 2017) attached in Section 13 of the IUCLID 6 dossier.

A reliable algal effects study is available for the siloxane D5 (CAS 541-02-6) and is read-across to Impurity 1 (Vi5-D5). This study (96-h, static test withPseudokirchneriella subcapitata(formerlySelenastrum capricornutum) gave a result 96-h EC50>12 µg/l and 96-h NOEC ≥12 µg/l. Effects were not seen within the limit of solubility in test media.

A reliable algal effects study is available for the siloxane D3 (CAS 541-05-9) and is read-across to Impurity 2 (Vi3-D3). This study (72-h, static test withPseudokirchneriella subcapitata) gave a result 72-h EC50>1.6 mg/l and 72-h NOEC ≥1.6 mg/l. Effects were not seen within the limit of solubility in test media.